Doesn't Google/Alphabet have their very own TLD that could use instead? Then it'd be very obvious what is/isn't official.
Given that that domain was registered in 2008, they probably have just been using this one for so long that it's not worth the hassle to switch now that they have the TLD.
It's good. The certificate is also valid for .apps.google and .appspot.com, and is issued by Google Trust Services LLC.
> Google Trust Services LLC
Which confusingly, is under the TLD .goog instead of .google, for god knows what reason...